linux-kernel - Re: [patch 2/8] PCI/MSI: Mask all unused MSI-X entries

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Message-ID: <87eebi3gay.ffs@nanos.tec.linutronix.de>
Date:   Wed, 28 Jul 2021 12:04:37 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Marc Zyngier <maz@...nel.org>
Cc:     "Raj\, Ashok" <ashok.raj@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Kevin Tian <kevin.tian@...el.com>,
        Ingo Molnar <mingo@...nel.org>, x86@...nel.org
Subject: Re: [patch 2/8] PCI/MSI: Mask all unused MSI-X entries

On Thu, Jul 22 2021 at 14:46, Marc Zyngier wrote:
> On Wed, 21 Jul 2021 23:57:55 +0100,
> Thomas Gleixner <tglx@...utronix.de> wrote:
>> msix_mask_all() is invoked before the msi descriptors are
>> allocated. msi_desc::masked is actually a misnomer because it's not like
>> the name suggests a boolean representing the masked state. It's caching
>> the content of the PCI_MSIX_ENTRY_VECTOR_CTRL part of the corresponding
>> table entry. Right now this is just using bit 0 (the mask bit), but is
>> that true forever? So we actually should rename that member to
>> vector_ctrl or such.
>
> To follow-up with this forward looking statement, should we only keep
> bit 0 when reading PCI_MSIX_ENTRY_VECTOR_CTRL? I.e.:
>
> 	entry->masked = (readl(addr + PCI_MSIX_ENTRY_VECTOR_CTRL) &
> 			 PCI_MSIX_ENTRY_CTRL_MASKBIT);
>
> Or do we want to cache the whole register? In which case I'm all for
> the suggesting renaming (though 'masked' is shared with the old-school
> multi-MSI).

We want to cache the whole register because that's what we need to write
when the mask bit is toggled.

Thanks,

        tglx